The present invention relates to a nucleic acid encoding a viral structural protein and the use of the nucleic acid or protein for diagnostic or vaccine purposes.
Infectious Salmon Anaemia (ISA) is a disease caused by a virus (ISAV) that belongs to the family Orthomyxoviridae. The disease is characterised by severe anaemia, leucopenia, ascites, haemorrhagic liver necrosis and petecchia of the vicera. The gills are pale, and petecchia of the skin is also common. The spleen is dark and swollen (Speilberg et al, 1995; Veterinary Pathology, 32, pp. 466-478). The virus replicates in endothelial cells, both in blood vessels and in the heart, and in polymorphonuclear leukocytes. Budding of the virus from pillar cells in the gills has been observed, indicating that gills are probably an important portal of entrance for ISAV.
ISA was observed for the first time in Norway (Thorud et al., 1988; Bull. Eur. Ass. Fish Pathol., 8 (5), pp. 109-111) and severe outbreaks have recently been diagnosed also in Scotland, the Shetland Islands and Canada. Mortality during outbreaks varies between 10 and 100% and younger individuals appear to be more susceptible than older individuals. However, high mortality has also been observed among market size fish. Clinical outbreaks have been observed so far in Atlantic salmon, but rainbow trout and brown trout may act as carriers of the agent without developing clinical signs. Despite stamping out strategies, new outbreaks occur regularly and result in significant losses.
Control of the disease therefore has a high priority, and the present invention provides novel means to carry out such control. The present invention provides for a nucleic acid encoding a structural protein, designated Structural Protein-1 (SP-1) of the ISAV and fragments of said protein. The nucleic acid comprises 1851 nucleotides and is depicted in SEQ ID NO 1; the deduced amino acid sequence of SP-1 is depicted in SEQ ID NO 2. The cloning and characterisation of the nucleic acid according to the invention provides for the production of the SP-1 of the ISAV using recombinant technology (Sambrook et al., Molecular cloning: a Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, 1989). Cloning techniques and subsequent protein expression using in vitro expression systems are well known in the art. In this way, recombinant SP-1 can be obtained, which is substantially free from other ISAV proteins. SP-1 was found to be specific for the ISA virus, which makes this protein very suitable for use in vaccinations and diagnostics. This isolated SP-1 can be used in the manufacture of vaccines to protect fish against infection with ISA virus. The vaccines may be used as marker vaccine to distinguish vaccination from field infections with ISAV. Alternatively, the nucleic acids encoding the SP-1 can be used to manufacture DNA vaccines or vector vaccines to protect fish against infection with ISAV. The nucleic acids and recombinant proteins of the present invention can furthermore be used for diagnostic purposes, for instance, to detect the presence of the ISAV or anti-ISAV antibodies in fish. Additionally, the recombinant SP-1 of the present invention can be used to produce ISAV specific antibodies. These antibodies can also be used for diagnostic purposes such as for detecting of ISAV in fish.